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The ultrasonic velocity, density and viscosity have been measured for the ternary mixtures of benzene, chlorobenzene and nitrobenzene with N-N dimethylformamide (DMF) in cyclohexane at 303K. The experimental data have been used to calculate the acoustical parameters namely adiabatic compressibility (β), free length (Lf), free volume (Vf), internal pressure (πi), viscous relaxation time (τ), Gibbs’ Free Energy (∆G*) and acoustic impedance (Z). The excess values of some the above parameters are also evaluated and discussed in the light of molecular interaction in the mixtures. It is observed that a weak molecular interaction prevailing in the present systems of the mixtures. Such interactions are primarily due to weak dipole-dipole and dipole- induced dipole types. Dispersive forces are also found to exist between the components of the mixtures.

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Journal of Chemical and Pharmaceutical Research

____________________________________________________

J. Chem. Pharm. Res., 2010, 2(1): 327-337

ISSN No: 0975-7384

Intermolecular Interaction Studies in Organic Ternary Liquid

Mixtures by Ultrasonic Velocity Measurements

S. Thirumaran*, S. Sudha

*Department of Physics (DDE), Annamalai University, Annamalainagar-608 002, India

__________________________________________________________

Abstract

The ultrasonic velocity, density and viscosity have been measured for the ternary mixtures of

benzene, chlorobenzene and nitrobenzene with N-N dimethylformamide (DMF) in cyclohexane

at 303K. The experimental data have been used to calculate the acoustical parameters namely

adiabatic compressibility (β), free length (Lf), free volume (Vf), internal pressure (πi), viscous

relaxation time (τ), Gibbs’ Free Energy (∆G*) and acoustic impedance (Z). The excess values of

some the above parameters are also evaluated and discussed in the light of molecular interaction

in the mixtures. It is observed that a weak molecular interaction prevailing in the present systems

of the mixtures. Such interactions are primarily due to weak dipole-dipole and dipole- induced

dipole types. Dispersive forces are also found to exist between the components of the mixtures.

Key Words: intermolecular free length, aprotic, internal pressure, Gibb’s free energy

______________________________________________________________________________

Introduction

Investigations on being binary and ternary mixtures of non-electrolytes by calculating excess

thermodynamic parameters are found to be highly useful in understanding the solute-solvent

interactions in these mixtures. Ultrasonic wave propagation affects the physical properties of the

medium and hence, can furnish information on the physics of the liquid and liquid mixtures. The

measured ultrasonic parameters are being extensively useful to study intermolecular processes in

liquid systems.[1-3] The sign and magnitude of the non-linear deviations from ideal values of

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______________________________________________________________________________

velocities and adiabatic compressibilities of liquid mixtures with composition are attributed to

the difference in molecular size and strength of interaction between unlike molecules.[4]. The

present investigation related on thermodynamic properties of binary as well as ternary liquid

mixtures of containing N-N dimethylformamide (DMF). DMF is a versatile compound. It is a

non-aqueous solvent which has no hydrogen bonding in pure state. Therefore, it acts as an

aprotic protophylic medium with high dielectric constant and it is considered as dissociating

solvent.[5]Binary and ternary mixtures of DMF with aromatic solvents are of interest in studies

of polymer miscibility, polymer phase diagrams and preferential interactions of polymers in

mixed solvents.[6-8]Therefore, a better understanding of the physico-chemical properties of

mixed solvent systems I-DMF + cyclohexane + benzene, II-DMF + cyclohexane +

chlorobenznene, and III-DMF + cyclohexane + nitrobenznene may help in the study of chemical

and biological processes in these media. Moreover, no ultrasonic or volumetric behaviour of

these mixtures are reported so far.

Hence, the authors had gone to investigate the present study with aid of ultrasonic parameters

and some of its related excess values with a view to throw light on intermolecular interaction

between the component molecules of the mixtures.

The present ternary liquid systems taken up study at 303K are

System-I

DMF

+ cyclohexane

+ benzene

System-II

DMF

+ cyclohexane

+ chlorobenzene

System-III

DMF

+ cyclohexane

+ nitrobenzene

Materials and Methods

Experimental Section

The chemicals used in the present work were analytical reagent (AR) and spectroscopic reagent

(SR) grades with minimum assay of 99.9% were obtained from Sd fine chemicals India and E-

merck, Germany. In all systems, the various concentrations of the ternary liquid mixtures were

prepared in terms of mole fraction, out of which the mole fraction of the second component

cyclohexane (X2 = 0.4) was kept fixed while the mole fractions of the remaining two (X1 and

X3) were varied from 0.0 to 0.6. There is nothing significant in fixing the second component at

0.4. The density of pure liquids and liquid mixtures are determined using a specific gravity bottle

by relative measurement method with a reproducibility of ± 0.01 kg.m-3 (Model: SHIMADZU

AX-200).An Ostwald’s viscometer of 10ml capacity is used for the viscosity measurement of

pure liquids and liquid mixtures and efflux time was determined using a digital chronometer to

within ±0.01sec. An ultrasonic interferometer (Model: F81) supplied by M/s. Mittal Enterprises,

New Delhi, working at a frequency 3MHz with an overall accuracy of ± 2 ms–1 has been used

for velocity measurement. An electronically digital constant temperature bath (RAAGA

Industries, Chennai) has been used to circulate water through the double walled measuring cell

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S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

made up of steel containing experimental mixtures at the desired temperature. The accuracy in

the temperature measurement is ± 0.1K.

Results and Discussion

The experimentally determined values of density (ρ), viscosity (η) and ultrasonic velocity (U) of

three liquid ternary systems at 303K are presented in Table 1. The values of adiabatic

compressibility (β), free length (Lf), free volume (Vf), internal pressure (πi) for the three liquid

systems are reported in Table2. Further relaxation time (τ), Gibb’s free energy (∆G*) and

acoustic impedance (Z) for all the ternary mixtures have been computed and reported in Table 3.

The excess values of adiabatic compressibility (βE), excess free length( LfE), excess free volume

(VfE), and excess internal pressure (πiE) are furnished in Table 4.

Table 1 Density (ρ ρ ρ ρ), viscosity (η η η η) and velocity (U) at 303 K

Mole Fraction

DENSITY

ρ ρ ρ ρ/(kg/m3)

VISCOSITY

η η η η/(×10-3 NSm-2)

VELOCITY

U/(m/s)

X1

X3

FOR SYSTEM-I

0.0000

0.5999

824.93

0.6530

1225

0.1060

0.9960

832.03

0.6644

1228

0.1177

0.4712

888.99

0.6920

1231

0.3146

0.2937

943.24

0.8248

1234

0.4150

0.1942

949.13

0.9417

1236

0.5259

0.0609

954.56

1.0320

1244

0.6001

0.0000

959.45

1.0695

1246

FOR SYSTEM-II

0.0000

0.6000

926.60

0.7676

1224.0

0.0999

0.4994

941.28

0.8318

1229.0

0.2999

0.4000

954.00

0.8606

1233.0

0.2999

0.2999

960.05

0.8941

1238.0

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S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

0.4000

0.1999

966.70

0.9729

1241.0

0.5001

0.0998

972.40

1.0473

1244.7

0.6001

0.0000

977.14

1.0830

1246.2

FOR SYTEM-III

0.0000

0.4342

1002.55

1.1015

1282.0

0.0999

0.5000

1006.86

1.1376

1294.0

0.1999

0.4000

1009.50

1.1754

1309.3

0.2999

0.2999

1012.10

1.2368

1324.2

0.4000

0.2000

1016.60

1.2736

1332.0

0.5000

0.1000

1021.60

1.3170

1341.1

0.6000

0.0000

1024.50

1.3384

1347.6

It is evident from the Table 1 that the density (ρ), viscosity (η) and ultrasonic velocity (U)

increases with increasing molar concentration of DMF in all the three liquid systems. The

pronounced increase or decrease in these parameters with composition of mixtures indicates the

presence of interactions between the component molecules in the ternary mixtures. DMF, the

widely organic solvent is an aprotic, protophylic, potentially basic medium. Additionally, DMF

can serve as a model compound of peptides to obtain information on protein systems.[9]

DMF itself being a polar molecule. When it is associated with substituted benzenes such as

benznene, chlorobenzene and nitrobenzene and the mixtures formed by these combinations have

not only dipolar-dipolar interaction between DMF molecules, but also the interaction of dipolar-

induced dipolar between DMF molecules and the substituted benzene molecules. The interaction

between unlike molecules seems to be stronger than the intra-molecular interactions and it

leads to decrease of interaction of molecule. In addition, the relatively small size of DMF as well

as its linear aliphatic configuration may be another factor contributing to the volume contraction

of the mixtures.

When DMF is in association with benzene, DMF being a polar one where both benzene and the

cyclohexane are non-polar. Mixing of benzene/cyclohexane with DMF tends to break

DMF-DMF dipolar association releasing several DMF dipoles. Consequently, the free dipoles of

DMF would induce moments in the neighboring molecules (cyclohexane/benzene), resulting in

dipolar-induced dipole interaction leading to contraction in volume. This leads to subsequent

decrease in adiabatic compressibility (β), and as well as in intermolecular free length (Lf) is

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______________________________________________________________________________

observed in all the three liquid systems, with the increasing molar concentration of DMF, which

is evident from the Table 2.

Table 2 Adiabatic compressibility (β β β β), Free length (Lf) Free volume (Vf) and Internal

pressure (π π π πi) at 303 K

Internal

pressure

π π π πi/(×106 Nm–2)

Mole Fraction

Free volume

Vf/(×10–7m3

mol–1)

Adiabatic

compressibility

β β β β/(×10–10 m2 N-1)

Free length

Lf/(×10-10 m)

X1

X3

FOR SYSTEM-I

0.0000

0.5999

8.0780

0.5671

2.0893

364.30

0.1060

0.9960

7.9710

0.5587

2.0222

409.68

0.1177

0.4712

7.4231

0.5436

1.6983

421.85

0.3146

0.2937

6.9620

0.5264

1.4430

503.67

0.4150

0.1942

6.8960

0.5239

1.1714

544.00

0.5259

0.0609

6.7690

0.5191

1.0085

554.34

0.6001

0.0000

6.7130

0.5169

0.9653

587.98

FOR SYSTEM-II

0.0000

0.6000

7.2035

0.5355

2.3070

284.79

0.0999

0.4994

7.0335

0.5291

1.9381

396.15

0.2999

0.4000

6.8948

0.5239

1.7398

425.78

0.2999

0.2999

6.7961

0.5201

1.5487

454.86

0.4000

0.1999

6.7168

0.5171

1.2796

504.80

0.5001

0.0998

6.6378

0.5140

1.0170

554.80

331

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S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

0.6001

0.0000

6.5897

0.5122

0.9447

599.53

FOR SYTEM-III

0.0000

0.4342

6.069

0.4915

1.575

413.76

0.0999

0.5000

5.9314

0.4859

1.4185

443.90

0.1999

0.4000

5.7785

0.4796

1.2742

476.27

0.2999

0.2999

5.6363

0.4737

1.1730

513.12

0.4000

0.2000

5.5442

0.4698

0.9856

560.21

0.5000

0.1000

5.4424

0.4654

0.8662

610.29

0.6000

0.0000

5.3748

0.4625

0.7761

661.45

Also, in particular, in the DMF + cyclohexane + chlorobenzne system, the chlorobenzene

molecules which are quite polar (µ = 1.54 D)[10] The chlorine atom being an electron

withdrawing atom, attracts the π-electrons of the benzene ring in C6H5Cl molecules and thus

decrease of electron density of the ring. This makes the benzene ring a relatively poor electron

donor towards the cyclohexane molecules, thereby a weak interaction between chlorobenzne

and cyclohexane is expected.

On the other hand, a dipole-dipole interaction between DMF and chlorobenzene seems to be

significant, which suggest that dipole-dipole interaction between them predominates in these

systems. Similar observations were noticed by earlier workers supports the present study.[11]

Similarly in the system-III, it is noticed that DMF and nitrobenzene mixtures are characterised

by the interactions between the π-electrons cloud of benzene ring with the delocalised π-electron

cloud over the nitrogen and oxygen atoms of the nitro group of nitrobenzene resulting in the

formation of weak interactions between them.[12]

Further, Cyclohexane belongs to alicyclic hydrocarbon (closed chain). The packing of carbon

atoms in this even numbered alkane group allows the maximum intermolecular attractions[13]

and therefore these molecules are highly inert towards an electrophile or nucleophile at ordinary

temperature. In the present study, among the three components, Cyclohexane is not expected to

involve in any interactions either with DMF or with other components due to its non-polar

nature. Further. Dispersive types of interactions are expected between the other components and

cyclohexane due to the non-polar nature of the cyclohexane and its inertness towards the electron

donors.[14]

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S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

Further, a decrease in free volume and an increase in internal pressure with increase in

concentrations of DMF is observed, which may be attributed to increasing magnitude of

interactions27 which are evident from the Table 2.

Table 3 Viscous relaxation time (Vτ τ τ τ), Gibb’s free Energy (∆ ∆ ∆ ∆G) and Acoustic

impedance (Z) at 303 K

Mole Fraction

Viscous

relaxation time

τ τ τ τ/(×10–12 S)

Gibb’s free energy

∆ ∆ ∆ ∆G*/(×10-20 KJ mol-1)

Acoustic impedance

Z/(×106 kg m2 s—1)

X1

X3

FOR SYTEM-I

0.0000

0.5999

0.7031

0.6235

1.0105

0.1060

0.9960

0.7124

0.6231

1.0217

0.1177

0.4712

0.7255

0.6358

1.0943

0.3146

0.2937

0.7644

0.6582

1.1639

0.4150

0.1942

0.8656

0.7105

1.1731

0.5259

0.0609

0.9312

0.7411

1.1874

0.6001

0.0000

0.9571

1.2330

1.1954

FOR SYTEM-II

0.0000

0.6000

0.7370

0.40260

1.1342

0.0999

0.4994

0.7798

0.66684

1.1568

0.2999

0.4000

0.7908

0.6727

1.1763

0.2999

0.2999

0.8100

0.7179

1.1885

0.4000

0.1999

0.8710

0.7132

1.1997

0.5001

0.0998

0.9266

0.7390

1.2104

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S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

0.6001

0.0000

0.9513

0.7506

1.2115

FOR SYSTEM -III

0.0000

0.4342

0.8911

0.7227

1.2852

0.0999

0.5000

0.8994

0.7265

1.3029

0.1999

0.4000

0.9054

0.7293

1.3217

0.2999

0.2999

0.9118

0.7323

1.3402

0.4000

0.2000

0.9412

0.7456

1.3541

0.5000

0.1000

0.9554

0.7518

1.3701

0.6000

0.0000

0.9589

0.7534

1.3806

From Table 3, it is observed that the relaxation time (τ) increases continuously with increase

in mole fraction of DMF. The relaxation time, which is of the order of 10

structural relaxation process [15] and such situation suggests that the molecules get rearranged

due to co-operation process[16]. The Gibb’s free energy (∆G*) (Table 3) increases

with increase in composition of DMF in all the three systems. The increasing values of

Gibb’s function suggest that the closer approach of unlike molecules is due to hydrogen bonding

[17-18]. The increase in ∆G* in all the mixtures indicates the need for shorter time for the co-

operative process or the rearrangement of the molecules in the mixtures.[19]

Further,

in

all

three

liquid

systems,

(Z) is found to be increased, which are listed in Table 3. when an acoustic wave travels

in a medium, there is a variation of pressure from particle to particle. The ratio of the

instantaneous pressure excess at any particle of the medium to the instantaneous velocity of that

particle is known as ‘specific acoustic impedance’ of the medium. This factor is governed by the

inertial and elastic properties of the medium. It is important to examine specific acoustic

impedance in relation to concentration and temperature. When a plane ultrasonic wave is set up

in a liquid, the pressure and hence density and refractive index show specific variations with

distance from the source along the direction of propagation. In the present investigation, it is

observed that these acoustic impedance (Z) values increase with increasing concentration of

DMF. Such an increasing values of acoustic impedance (Z), further supports the possibility of

molecular interactions between the unlike molecules.

In order to understand the nature of molecular interactions between the components of the liquid

mixtures, it is of interest to discuss the same in term of excess parameter rather than actual

values. Non-ideal liquid mixtures show considerable deviation from linearity in their physical

behaviour with respect to concentration and these have been interpreted as arising from the

–12 seconds, is due to

the

values

of

acoustic

impedance

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______________________________________________________________________________

presence of strong or weak interactions. The extent of deviation depends upon the nature of the

constituents and composition of the mixtures. The excess values of adiabatic compressibility

(βE), free length (LfE), free volume (VfE) and internal pressure (πiE) for all the three liquid

systems are furnished in Table 4.

Table 4 Excess values of Adiabatic compressibility (β β β βE), Free length (Lf

(Vf

E) Free volume

E) and Internal pressure (π π π πi

E) at 303 K

Mole Fraction

Excess free

volume

Vf

mol–1)

Excess internal

pressure

π π π πi

Excess free

length

Lf

Excess adiabatic

compressibility

β β β βE/(×10–10 m2 N-1)

E /(×10–7m3

E /(×10-10 m)

E /(×106 Nm–2)

X1

X3

FOR SYSTEM-I

0.0000

0.6000

0.3125

0.0117

0.5385

14.63

0.1004

0.4988

0.4098

0.0115

0.473

1.23

0.1998

0.4001

0.0654

0.0048

0.1497

1.66

0.3000

0.3000

0.1527

0.0544

0.1644

37.69

0.4000

0.3000

0.0859

0.064

0.0473

78.02

0.5000

0.0999

0.0231

0.0965

0.0288

80.79

0.6002

0.0000

0.1781

0.0103

0.1154

109.64

FOR SYSTEM-II

0.0000

0.6000

0.1655

0.0085

0.2971

3.80

0.1000

0.5000

0.0765

0.0556

0.0068

3.18

0.1991

0.4001

0.0244

0.0042

0.0399

0.94

0.3000

0.3001

0.2025

0.0035

0.0708

24.28

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S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

0.4000

0.2000

0.0009

0.0041

0.4326

74.22

0.5001

0.1998

0.6207

0.024

0.0008

89.36

0.6001

0.0000

0.0479

0.0062

0.0220

121.19

FOR SYSTEM-III

0.0000

0.5657

0.1679

0.0100

-0.5488

16.45

0.0999

0.5001

1.0430

0.0056

-0.6613

36.58

0.2998

0.4000

0.7937

0.0074

-0.7745

52.86

0.3999

0.3999

0.584

0.0147

-2.7025

87.68

0.3999

0.4000

0.3954

0.0108

-1.1393

134.90

0.5000

0.1000

0.2052

0.0012

-0.7859

146.17

0.6000

0.0000

0.0475

0.0006

-0.7689

183.72

It is learnt that the dispersion forces are responsible for possessing positive excess values, while

dipole-dipole, dipole-induced dipole, charge transfer interaction and hydrogen bonding between

unlike molecules are responsible for possessing negative excess values.[20].In the present study,

the excess values of adiabatic compressibility (βE) and intermolecular free length (LfE) which are

given in Table 4 whose values exhibit positive deviations over the entire range of composition in

all the three liquid systems. This suggests that in addition to dipole-dipole and dipole-induced

dipole interactions, dispersive forces are also operative in all these systems. It has been reported

that dispersive forces tend to make a positive contribution to the excess functions is obvious.[1-

3]The positive values further attribute that apart from dispersion forces, weak dipolar forces

are also operating with some specific interaction between molecules of the mixtures. Since

dispersive interactions [21-23] are dominant between benzene and cyclohexane, same types of

interaction may also play between chlorobenzene, nitrobenzene and cyclohexane and its

inertness towards the electron donors.

The excess values of internal pressure (πiE) which are furnished in the Table 4. The positive

values of this parameter over the entire range of composition in all the three liquid systems

clearly supporting this.

Conclusion

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s thirumaran et al j chem pharm res 2010 9

S. Thirumaran et al J. Chem. Pharm. Res., 2010, 2(1): 327-337

______________________________________________________________________________

From the present investigation, it is obvious that there exists a molecular association between the

components of the mixtures. In specific, a weak molecular interaction prevailing in

the present systems of the mixtures. Such interactions are primarily due to weak dipole-dipole

and dipole- induced dipole types. Dispersive forces are also found to exist between the

components of the mixtures.

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